tsan: fix a bug memory access handling

We incorrectly replaced shadow slots
when the new value is not stronger than the old one.
The bug can lead to false negatives.
The bug was detected by Go race test suite:
https://github.com/golang/go/issues/10589



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@236008 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed